I have a potted avocado plant that I grew from seed, and it recently started to get curled leaves. While I had an idea of what was causing it, I wanted to dive a bit deeper and make sure I knew exactly what the issue was. Here’s what I found.
Avocado trees get curled leaves from over-watering, high salt and chlorine content, bound roots, transplant shock, or improper nutrients. However, the most common causes are due to over-watering and high amounts of salt and chlorine. For best results, only water when the soil is dry and use soft waters like rainwater.
So, while avocado trees get curled leaves for several reasons, how can we tell which issue is causing it, and how can we fix it? Let’s take a closer look.
1. Over or Under-Watering
Avocado trees are easy to over and under-water, especially if they have soils that have poor or excess drainage. To prevent both over and under-watering, make sure the soil is well-draining and only water when the soil is dry. After, apply 2 inches of compost and mulch to help protect the soil and retain water.
Poor drainage is common in soils that are high in clay as the tightly packed particles allow little water to escape. If left for too long, the avocado tree’s leaves begin to curl from the stress of deprived oxygen in the soil, and the stagnant water begins to rot the roots. This disease is commonly called root rot and can kill the avocado tree.
On the other hand, excess drainage often is from soils that have too much sand, which lets the water runoff before the avocado tree can absorb it. Without enough water, the avocado tree’s leaves curl to retain moisture and start browning and dropping. These symptoms is made worse if the tree is overexposed to strong sunlight.
For a good visual of the particle size of sand vs clay, check out the graphic below.
So, what’s the best soil type for avocado trees?
Ideally, since avocados are natively from a tropical climate, they prefer sandy, loamy soil. This means a balance of sand, clay, and silt.
Each type of soil (sand, clay, and silt) has its pros and cons. To achieve all of the pros and minimize all of the cons, garden soil should be a mix of all three materials—which is called loam soil.
|Sand||Good drainage||Doesn’t hold nutrients well|
|Silt||Holds nutrients well||Poor drainage|
|Clay||Holds the most nutrients||Even worse drainage than silt|
If you’d like to learn more about the best soil mix for avocado trees, you can visit my post here.
I also have a post on how to plant avocado trees in heavy clay soils: Can Fruit Trees Grow in Clay Soil (& How Do You Plant Them)?.
How to Fix Drainage and Watering Issues
You can test your soil’s drainage by digging a 1-foot by 1-foot hole nearby and filling it with water. If the hole drains slower than 2 inches per hour, it has poor drainage.
You can amend poorly draining soils by adding organic materials on top of the soil. These will be worked into the soil over time. For potted avocado trees with poor drainage, it’s sometimes better to simply repot it with fresh potting soil.
While you can dig up planted avocado trees (those not in pots or containers), it’s not recommended as it’s likely to lead to transplant shock. Instead, amending the soil from the top down is the best approach. Even though this method can take some time, it reduces the chance of further stressing the avocado tree.
Once you have well-draining soil, apply 2 inches of each compost and mulch within the drip line of the avocado tree. Keep the materials at least 3 inches away from the tree’s trunk to prevent mold.
This method also applies for soils that drain too quickly and can’t hold water. Here’s why.
Compost provides valuable nutrients to the soil and increases the soil’s richness and water retention. For example, every 1% increase in the soil’s richness can hold an additional 20,000 gallons of water per acre (source). It also feeds beneficial soil life such as earthworms and mycorrhizal fungi—which provide even more nutrients and disease resistance for the plant.
Mulch protects the soil (and the beneficial soil life) from drying out in the sun and wind. In hot and dry weather, mulch dramatically reduces evaporation and locks in moisture from the soil. In cold weather, mulch provides a layer of insulation for the tree and its roots. Some good mulches for avocado trees are leaves, bark, pine needles, and straw.
So, to recap:
Once you have well-draining soil, only water avocado trees when the first 2-4 inches of soil are dry. I check for this by pushing a finger into the soil. Then, apply 2 inches of each compost and mulch under the drip line of the tree, keeping them at least 3 inches from the trunk. Reapply compost every 1-2 months.
Generally, this means watering about once a week. But weather, soil, tree size, and other factors can change how often you need to water. Because of this, the better rule is to wait for the soil to dry before watering.
However, while you can water the right amount and at the right time, something that’s not often considered is the type of water.
2. High Salt Content
Salt that’s accumulated in the soil can dry, curl, and brown the leaves on avocado trees. This eventually leads to leaf drop. To remove salt from the soil, use either soft water, vinegar, or chemical amendments. However, the easiest options to remove salt are deep watering with soft water or using vinegar.
Salt and chlorine build-up (more on chlorine later) is especially common for potted avocado plants since they have a limited amount of soil to work with. Because of this, small amounts of salt and chlorine can quickly become potent. Generally, Hass avocados are more affected by this than Reed or other varieties.
There are many types of salts found in most water sources. For context, here are some of the most common salts found in hard waters, such as tap and irrigation water (don’t worry, you don’t need to memorize these).
The problem with this is the salts from tap water and fertilizer build up over time in the soil and the leaves. When the water evaporates from the soil and the leaves, salt is left behind. The extra salt then dries out the avocado leaves starting from the tips, curling the leaves and turning them brown.
While an excess of salt typically doesn’t affect many plants, avocado trees are particularly sensitive to it, as well as chlorine. This is why avocado leaves curl, brown, and drop while other plants continue to do well with the same soil and water.
Fortunately, there are a few ways you can remove or reduce the salt in the water you irrigate with.
How To Fix Excess Salts in the Soil
- Deep Watering
- Soft Waters
- Chemical Amendments
By far the easiest and most feasible way to reduce or remove the salts in water is by deep watering (also called leaching). By providing your avocado tree with deep watering, you’re using excess water to dissolve the salt and disperse it further into the soil (ideally beyond 3-4 feet, which is a common depth for roots).
You can deep water your avocado tree by providing about 15-30 minutes of light to moderate watering whenever the soil is dry. This helps soak the soil thoroughly and allows the salts to leach through the soil.
Some other ways to flush the salt from the soil are to use soft water, vinegar, or by adding chemical amendments. While using soft water and vinegar are fairly easy to do, chemical amendments are a bit more complex and sometimes not organic.
Tap and irrigation water are often hard waters, meaning they have excess salts and chemicals (such as chlorine) in them from the treatment plants. While this helps disinfect water, and make it possible to transport it long distances, these salts and chemicals accumulate in the soil over time.
To combat this, water your avocado trees with soft waters, such as:
- Reverse Osmosis (RO)
As mentioned, avocado trees are more sensitive to these build-ups than other plants, which is why you might only be seeing a problem with your avocado trees.
While reverse osmosis water is a bit harder to come by, rainwater and distilled (steam water) are fairly easy to obtain. You can capture rainwater, use water from lakes and rivers, or use distilled water.
Moving on, let’s take a look at which chemical amendments would help remove the salts and how to test for salts.
- Calcium chloride
- Sulfuric acid
- Iron sulfate
- Aluminum sulfate
- Lime-sulfur solution
Again, I wouldn’t recommend this option for beginners. However, if you are interested in pursuing chemical amendments for your avocado tree’s soil, know that I haven’t tested any of these amendments personally, so I’d suggest consulting this article by Texas A&M University to learn more.
How To Test For Salt in the Soil
If you believe you have a salt build-up in your soil and would like to test it to confirm, you can send it out to a testing laboratory, such as your local cooperative extension. For example, here in Texas, I can send a soil sample to the Texas A&M AgriLife Extension Service.
On the other hand, if you’re interested in conducting a salinity test at home, then check out this video by NDSU Soil Health to see how it’s done. I wasn’t able to find the soil salinity tester she used, but I found a similar one on Amazon. It’s a little pricey, but it could be worth it if you have a stubborn salinity issue.
3. High Chlorine Content
Chlorine is commonly used to treat tap and irrigation water and easily accumulates in the soil after watering. Like salt, chlorine in the soil is also stored in the avocado tree’s leaves, causing them to curl, brown, and drop. To fix this, use soft waters, charcoal filters, evaporation.
Some types of water have less chlorine than others. Here are some examples of high and low chlorinated water.
|High Chlorine Water||Low Chlorine Water|
|Tap water||Rain, Distilled, or RO water|
|Irrigation water||Chlorine-evaporated water|
|Most other treated waters||Charcoal-filtered water|
If you’re already going to use soft waters such as rainwater, distilled water, or RO water, you can simply skip this next section.
However, if you’re using tap or irrigation water for your avocado trees, I recommend following the next steps to reduce or remove the chlorine from your avocado tree’s water.
How To Reduce Chlorine in Water
Aside from using soft water, there are two easy ways to remove chlorine from hard or tap waters:
- Charcoal filters
One of the easiest ways to remove chlorine from tap water is to let the chlorine evaporate. Generally, this means leaving the water to sit uncovered for 4.5 days (source). The greater the surface area, the faster the evaporation will occur. You can also boil the water first to speed up this process.
Additionally, you can use a charcoal filter to remove chlorine. Brita filters have a charcoal filter and will work fine for this purpose.
However, keep in mind that while these two methods remove chlorine, they don’t remove chloramines. Because of this, there’s still a small chance your avocado tree can get chemically burned and have curled or browned leaves.
So, while chlorine-evaporation and charcoal filters are a good first step (and might be the only thing your avocado tree needs), consider adding a second step of performing reverse osmosis to completely remove the chloramines (source).
Or to keep it easy, you use soft water from the beginning.
Reverse osmosis systems can be expensive, so first check to see if your avocado tree gets better with chlorine-evaporated or charcoal-filtered water. If these methods don’t help, then consider adding reverse osmosis as well.
I personally get my reverse osmosis drinking water from the grocery store in 5-gallon jugs for $2.50 each. However, you can also get one installed in your house. If you’re interested, here’s a RO filter that my family uses from Amazon.
If you’d like to test the amount of chlorine in your water first, check out this video by Acuro Organics Limited.
4. Root Bound (Potted Trees)
Potted avocado trees that outgrow their container become root bound, leading to stress and symptoms such as curling and dropping leaves. Generally, potted trees should be repotted into a larger container every 3-5 years. Instead of repotting, you can prune the avocado tree’s roots, but it’s not recommended.
Moving on from water, root binding commonly occurs from avocado trees that outgrow their pot or container. This also includes avocado trees that are planted in the garden but have root barriers placed into the ground.
Avocado trees are fairly heavy feeders of both water and nutrients, and they can run out if they have a limited amount of soil to work with. When they start running low, their roots grow deeper and longer to search for these resources.
If these roots are then blocked by a container or root barrier, they’ll double back on themselves, and continue growing in the limited space. This root confinement stresses avocado trees and can reveal itself as issues such as leaf curl and drop, as well as fruit drop.
To avoid root binding, potted avocado trees need to be repotted into larger pots every 3-5 years. Also, to prevent collapsed soils or those with poor nutrients, fresh potting soil should be used. If you use a root barrier for your planted avocado trees, make sure it’s large enough to allow for sufficient root growth.
Generally, full-sized avocado tree roots require soil space that’s at least 3-4 feet deep and 7-10 feet wide.
While uncommon, root binding can occur in construction sites, or those that have previously had the ground flattened. Because of the compact ground, the roots have a hard time pushing through the soil and gathering water and nutrients.
Fortunately, compacted soils will become looser over time, when the plants’ roots and water permeate the ground.
5. Transplant Shock
If an avocado tree was recently planted or repotted, and it now has curled leaves, it’s likely due to transplant shock. Transplant shock occurs when the plant is exposed to a new environment and has to establish a new root system. Avoid transplanting unless necessary as it can take up to 1 year for recovery.
Like many plants, avocado trees are vulnerable to transplant shock. To help avoid this, I like to plant with the following steps in mind:
- Have the new ground (or pot) prepared
- Remove as much of the tree’s current topsoil as possible, without damaging the shallow roots
- Grab the base of the tree’s trunk and wiggle lightly
- Using your other hand, scoop up and support the rootball
- Lightly place the tree in the new ground (or pot) and fill it in
- Make sure the soil is at the same level on the trunk as before
- Apply 2 inches of compost and mulch to the top of the soil
- Water generously and add more soil as needed
Generally, as long as you avoid damaging and breaking the roots, and you keep your avocado tree comfortable during the move, the amount of stress from transplant shock will be reduced or eliminated.
6. Lack or Excess of Nutrients
Without sufficient nutrients, avocado trees cannot feed their leaves and keep them alive. This leads to leaves curling, discoloring, and dropping. Blossoms and fruit can also drop. For best results, use high nitrogen or balanced fertilizer, or compost. Generally, compost is better as it also promotes healthy soil.
Luckily, fertilizing avocado trees is a bit easier than some other fruit trees as they have the same needs as citrus trees. Because of this, you’ll often find citrus fertilizers that also have avocado trees on their label (see the image below).
The best fertilizer NPK (nitrogen, phosphorus, and potassium) for avocado trees is either one with double the nitrogen, such as a 6-3-3, or a balanced fertilizer, such as a 10-10-10.
However, while chemical fertilizers are effective at providing nutrients, they’re often too potent for the soil and contain harmful chemicals. This leads to the beneficial soil life dying off—turning living soil into dead dirt.
Side note: if you’d like to learn more about healthy soils, a great book/audiobook is Dirt to Soil by Gabe Brown.
Even though compost isn’t as nutrient-dense as chemical fertilizers, the nutrients it does have are more bioavailable and absorbable by the avocado trees (as well as the beneficial soil life). This also leads to more water retention in the soil, as mentioned in the above watering section.
This helpful soil life, including mycorrhizal fungi, help scavenge for deeper nutrients for the avocado tree, as well as provide it with more disease and pest resistance.
But nutrients aren’t everything.
Without a proper soil pH, avocado trees will be unable to absorb nutrients from the soil, causing growth issues such as curled and discolored leaves.
The reason why plants prefer a slightly acidic soil pH is because the acid helps dissolve the solid nutrients into nutrients that are usable by the plant’s finer roots.
As a result, avocado trees prefer slightly acidic soil that’s between a pH of 5.0-7.0 (source).
Two good ways to measure your soil’s pH are with pH strips or a pH meter. I prefer using a pH meter since they’re easy to use and affordable. To see which pH meter I use and recommend, visit my recommended tools page.
If you find that your avocado tree’s soil pH is too acidic (under 5.0), consider amending it with alkaline amendments such as wood ash, biochar, or lime powder. On the other hand, amend soil that’s too alkaline (above 7.0) with acidic materials such as coffee grounds, sand, or peat moss.
Also, if you’d like more information about the best fertilizers for avocado trees, check out my other post: Avocado Tree Fertilizers: The Full Guide & Top 3 Brands.
Once avocado trees have the proper nutrients and soil pH, they’ll start growing new leaves.
While this can be a lot of information to sort through, I found that my avocado tree was getting curled leaves from a lack of water. However, in my research, I found that many avocado tree growers also had issues with salts and chlorine.
If you don’t know where to start, start simple.
Start by only watering when the soil is dry and provide quality compost instead of fertilizers (which can cause salts to build up).
After, check for any root binding or any chance of transplant shock. These two potential issues are fairly easy to eliminate as they normally only occur for potted avocado trees or those that have been recently transplanted.
If you’ve checked and tried these options, then the only thing left is to reduce or eliminate possible salts and chlorine from the soil. This can be done easily if you water the avocado tree with soft water and in deep watering sessions to leach the salts and chemicals through the soil.
However, if you still get stuck, and still can’t determine the cause or solution of the curling leaves on your avocado tree, contact your local nursery, professional orchard, or cooperative extension service. They’ll be able to help review your soil as well as the specific issues avocado trees get in your region.